Various processes for microencapsulation, and exemplary methods and materials are set forth in Schwantes (U.S. Pat. No. 6,592,990), Nagai et. al. (U.S. Pat. No. 4,708,924), Baker et. al. (U.S. Pat. No. 4,166,152), Wojciak (U.S. Pat. No. 4,093,556), Matsukawa et. al. (U.S. Pat. No. 3,965,033), Matsukawa (U.S. Pat. No. 3,660,304), Ozono (U.S. Pat. No. 4,588,639), Irgarashi et. al. (U.S. Pat. No. 4,610,927), Brown et. al. (U.S. Pat. No. 4,552,811), Scher (U.S. Pat. No. 4,285,720), Shioi et. al. (U.S. Pat. No. 4,601,863), Kiritani et. al. (U.S. Pat. No. 3,886,085), Jahns et. al. (U.S. Pat. Nos. 5,596,051 and 5,292,835), Matson (U.S. Pat. No. 3,516,941), Chao (U.S. Pat. No. 6,375,872), Foris et. al. (U.S. Pat. Nos. 4,001,140; 4,087,376; 4,089,802 and 4,100,103), Greene et. al. (U.S. Pat. Nos. 2,800,458; 2,800,457 and 2,730,456), Clark (U.S. Pat. No. 6,531,156), Saeki et. al. (U.S. Pat. Nos. 4,251,386 and 4,356,109), Hoshi et. al. (U.S. Pat. No. 4,221,710), Hayford (U.S. Pat. No. 4,444,699), Hasler et. al. (U.S. Pat. No. 5,105,823), Stevens (U.S. Pat. No. 4,197,346), Riecke (U.S. Pat. No. 4,622,267), Greiner et. al. (U.S. Pat. No. 4,547,429), and Tice et. al. (U.S. Pat. No. 5,407,609), among others and as taught by Herbig in the chapter entitled “Encapsulation” in Kirk Othmer, Encyclopedia of Chemical Technology, V.13, Second Edition, pages 436-456 and by Huber et. al. in “Capsular Adhesives”, TAPPI, Vol. 49, No. 5, pages 41A-44A, May 1966, all of which are incorporated herein by reference.
More particularly, U.S. Pat. Nos. 2,730,456, 2,800,457; and 2,800,458 describe methods for capsule formation. Other useful methods for microcapsule manufacture are: U.S. Pat. Nos. 4,001,140; 4,081,376 and 4,089,802 describing a reaction between urea and formaldehyde; U.S. Pat. No. 4,100,103 describing reaction between melamine and formaldehyde; British Pat. No. 2,062,570 describing a process for producing microcapsules having walls produced by polymerization of melamine and formaldehyde in the presence of a styrenesulfonic acid. Microcapsules are also taught in U.S. Pat. Nos. 2,730,457 and 4,197,346. Forming microcapsules from urea-formaldehyde resin and/or melamine formaldehyde resin is disclosed in U.S. Pat. Nos. 4,001,140; 4,081,376, 4,089,802; 4,100,103; 4,105,823; and 4,444,699. Alkyl acrylate-acrylic acid copolymer capsules are taught in U.S. Pat. No. 4,552,811. Each patent described throughout this application is incorporated herein by reference to the extent each provides guidance regarding microencapsulation processes and materials.
Interfacial polymerization is a process wherein a microcapsule wall of a polyamide, an epoxy resin, a polyurethane, a polyurea or the like is formed at an interface between two phases. U.S. Pat. No. 4,622,267 discloses an interfacial polymerization technique for preparation of microcapsules. The core material is initially dissolved in a solvent and an aliphatic diisocyanate soluble in the solvent mixture is added. Subsequently, a nonsolvent for the aliphatic diisocyanate is added until the turbidity point is just barely reached. This organic phase is then emulsified in an aqueous solution, and a reactive amine is added to the aqueous phase. The amine diffuses to the interface, where it reacts with the diisocyanate to form polymeric polyurethane shells. A similar technique, used to encapsulate salts which are sparingly soluble in water in polyurethane shells, is disclosed in U.S. Pat. No. 4,547,429. U.S. Pat. No. 3,516,941 teaches polymerization reactions in which the material to be encapsulated, or core material, is dissolved in an organic, hydrophobic oil phase which is dispersed in an aqueous phase. The aqueous phase has dissolved materials forming aminoplast resin which upon polymerization form the wall of the microcapsule. A dispersion of fine oil droplets is prepared using high shear agitation. Addition of an acid catalyst initiates the polycondensation forming the aminoplast resin within the aqueous phase, resulting in the formation of an aminoplast polymer which is insoluble in both phases. As the polymerization advances, the aminoplast polymer separates from the aqueous phase and deposits on the surface of the dispersed droplets of the oil phase to form a capsule wall at the interface of the two phases, thus encapsulating the core material. This process produces the microcapsules. Polymerizations that involve amines and aldehydes are known as aminoplast encapsulations. Urea-formaldehyde (UF), urea-resorcinol-formaldehyde (URF), urea-melamine-formaldehyde (UMF), and melamine-formaldehyde (MF), capsule formations proceed in a like manner. In interfacial polymerization, the materials to form the capsule wall are in separate phases, one in an aqueous phase and the other in a fill phase. Polymerization occurs at the phase boundary. Thus, a polymeric capsule shell wall forms at the interface of the two phases thereby encapsulating the core material. Wall formation of polyester, polyamide, and polyurea capsules typically proceeds via interfacial polymerization.
U.S. Pat. No. 5,292,835 teaches polymerizing esters of acrylic acid or methacrylic acid with polyfunctional monomers. Specifically illustrated are reactions of polyvinylpyrrolidone with acrylates such as butanediol diacrylate or methylmethacrylate together with a free radical initiator.
Common microencapsulation processes can be viewed as a series of steps. First, the core material which is to be encapsulated is typically emulsified or dispersed in a suitable dispersion medium. This medium is typically aqueous but involves the formation of a polymer rich phase. Most frequently, this medium is a solution of the intended capsule wall material. The solvent characteristics of the medium are changed such as to cause phase separation of the wall material. The wall material is thereby contained in a liquid phase which is also dispersed in the same medium as the intended capsule core material. The liquid wall material phase deposits itself as a continuous coating about the dispersed droplets of the internal phase or capsule core material. The wall material is then solidified. This process is commonly known as coacervation.
U.S. Pat. No. 4,046,750 teaches an ionene modified polymeric bead. Dimethylamino substituted acrylic polymer is cross-linked and then the formed beads are reacted with a mixture of ditertiary amine and a dihalide to attach ionene segments to the tertiary amine centers on the beads. Insoluble cationic modified beads are formed. These cationic beads are useful in affinity chromatography.
Microcapsule Technologies in WO 01/41915 teaches coating formed anionic microcapsules by adding compounds with a cationic charge in a controlled manner. For example polyurea capsules are introduced to a solution of vinylpyrrolidone to coat the capsules and render them with cationic character. Similarly melamine microcapsules are taught to be coated with a homogenous solution of hydroxypropyl guar to impact cationic character. Gelatin capsules are illustrated coated with hydroxyethyl cellulose followed by epichlorhydrin to render them cationic.
Firmenich in EP 1637188 describes flowable dispersions of coacervate capsules based on acrylamido methylpropane sulfonate with a thickening polymer of nonionic and cationic polymers. A complex between the anionic aminoplast capsules and cationic polymer is though beneficial to drive the deposition of the capsules from rinse off formulations onto surfaces to which the capsules are applied.
Similar to the approach of Microcapsule Technologies, U.S. publication 2005/0112152 also teaches applying a second coating of a cationic material over an acrylamide and melamine formaldehyde based wall. Cationic polymer coated capsules are taught prepared by mixing uncoated fragrance containing capsules with a cationic polymeric deposition aid.
Each of the above methods is deficient to form cationic microcapsules of low permeance and/or rely on multiple layers making the processes unattractive commercially.
Unfortunately, capsules manufactured using the aforementioned methods and raw materials have several drawbacks which include: (1) they cannot be formulated in certain classes of products due to strict formulation limits, (2) they have high permeabilities when incorporated into products that contain high levels of surfactant, solvents, and/or water, which results in the premature benefit agent release, (3) they can only effectively encapsulate a limited breadth of benefit agents, and (4) they either are so stable that they do not release the benefit agent in use or have insufficient mechanical stability to withstand the processes required to incorporate them in and/or make a consumer product and (5) they do not adequately deposit on the situs that is being treated with consumer product that contains capsules.
Capsules made according to the invention can be made to better control permeability characteristics. Capsules made according to the invention are surprisingly better able to contain liquid contents without leakage over time. The capsules can be made less leaky than those made by comparable prior art processes. Alternatively permeability in certain applications is desired. Through selection of wall material and control of length of time of cross-linking or temperature of cross-linking, capsules can be made with differing permeability profiles from extremely tight with little to no leakage to capsules that have measurable permeability useful where a measurable release rate over time is desired.
The capsules according to the invention are useful with a wide variety of capsule contents (“core materials”) including, by way of illustration and without limitation, perfumes; brighteners; insect repellants; silicones; waxes; flavors; vitamins; fabric softening agents; skin care agents; enzymes; probiotics; dye polymer conjugate; dye clay conjugate; perfume delivery system; sensates in one aspect a cooling agent; attractants, in one aspect a pheromone; anti-bacterial agents; dyes; pigments; bleaches; flavorants; sweeteners; waxes; pharmaceuticals; fertilizers; herbicides and mixtures thereof. The microcapsule core materials can include materials which alter rheology or flow characteristics, or extend shelf life or product stability. Essential oils as core materials can include, for example, by way of illustration wintergreen oil, cinnamon oil, clove oil, lemon oil, lime oil, orange oil, peppermint oil and the like. Dyes can include fluorans, lactones, indolyl red, I6B, leuco dyes, all by way of illustration and not limitation. The core material should be dispersible or sufficiently soluble in the capsule internal phase material namely in the internal phase oil or soluble or dispersible in the monomers or oligomers solubilized or dispersed in the internal phase oil. When the internal phase is water, the core material should be dispersible or sufficiently soluble in the water phase. The invention is particularly useful to encapsulate volatile fragrances and flavorants. When a water phase is being microencapsulated, with the oil phase serving as the continuous phase, the core material should be soluble or dispersible in the water phase so as to form a dispersion in water that can be emulsified into the oil phase.
In alternative embodiments, capsules according to the invention are also able to be fashioned with thermoplastic polymeric materials resulting in low leakage heat sensitive capsules that could be opened with heat in addition to conventional techniques such as pressure, scraping, friction, shearing, impact, or other energy input. The capsules according to the invention can also be useful in applications with thermal print heads, or lasers, or other heating or impact elements. In alternative embodiments, if a light stimulated material is included, light sensitive capsules are also feasible.
The permeability characteristics of the capsules disclosed herein have versatility for a variety of applications. Wherever an internal phase is desired to be held securely over time but available to be exuded or released upon fracture or breakage of the capsules such as with application of pressure, a low permeability capsule according to the invention can be fashioned. Where measurable release is desired, more permeable capsules can also be fashioned. Where adhesion on surfaces such as textiles and anionic substrates is desired, cationic capsules can also be fashioned.